This invention discloses the use of certain Nα-long chain(C8 to C16) alkanoyl di basic amino acid alkyl (C1 to C4) ester salts with fatty acid (C8-C14) glycerol esters. Specifically the Nα-long chain alkanoyl di basic amino acid alkyl ester salts of interest are the Nα-long chain alkanoyl dibasic amino acid alkyl ester of L-arginine, L-histidine, L-tryptophan and L-lysine. The corresponding anion can be any anions that do not cause significant water insolubility and thereby prevent its effectiveness as an antimicrobial agent in aqueous or alcoholic solvents. Suitable anions include but are not limited to halides, sulfate, acetate, glycerophosphate, gluconate, mono- di- or tri-carboxylic acid, hydroxy carboxylic acid or mono and dihydrogen phosphates, phosphonates, phosphinates, and phenolates.
Although Nα-long chain alkanoyl di basic amino acid alkyl ester salts have been known since the 1960's, one of the first patents to recommend these amino acids, specifically for food applications was U.S. Pat. No. 3,825,560 (issued Jul. 23, 1979). A number of derivatives are disclosed including Nα-cocoyl-L-arginine ethyl ester pyrrolidone carboxylate and Nα-lauroyl-L-arginine methyl ester hydrochloride. Since this publication there has been several more patents issued or published disclosing specifically Nα-lauroyl-L-arginine ethyl ester hydrochloride salt (LAE). These include U.S. Pat. No. 5,780,658 that discloses a process to prepare LAE, as well as disclosing its use for food applications. U.S. Pat. No. 7,074,447 B2 discloses an antimicrobial composition comprising LAE with potassium sorbate. U.S. Pat. No. 7,087,769 is another process patent suggesting its use for food. Two patent publications, U.S. 2004/0166082 and U.S. 2004/0175350, disclosure di basic amino acid alkyl ester salts useful for cosmetic applications. U.S. 2004/0254232 covers oral care while U.S. 2004/0265443 covers food. U.S. 2005/0175747 discloses complexes formed between LAE and various anionic hydrocolloids. All of the above references are incorporated into the body of our present invention.
One of the purposes of this invention is to formulate a synergistic Nα-long chain alkanoyl di basic amino acid alkyl ester salt type biocide mixture that will overcome a significant shortcoming found in the sole use of Nα-long chain alkanoyl di basic amino acid alkyl ester salts. By combining glycerol esters of fatty acids, with chain lengths of from C6 to C14, significant broadening of cidal activity is found for the Nα-long chain alkanoyl di basic amino acid alkyl ester salts. Furthermore, this synergistic composition allows the use of much lower levels of either biocide while maintaining biocidal efficacy and thereby reducing cost.
A shortcoming of Nα-long chain alkanoyl di basic amino acid alkyl ester salts are their loss of anti-microbial activity and water solubility due to chemical/enzymatic hydrolysis of the ester functionality. This loss is dependent on a number of variables e.g., presence of lipases and/or esterases, and pH. It has been found that the chemical hydrolysis is particularly rapid at about pH4.0 or below or at about pH8.0 or above. Because in many applications the pH is in these critical ranges, Nα-long chain alkanoyl di basic amino acid alkyl ester salts need to have present other bioactive substances to maintain activity after the Nα-long chain alkanoyl di basic amino acid alkyl ester salts have hydrolyzed.
Also, Nα-long chain alkanoyl di basic amino acid alkyl ester salts have a strong tendency to form complexes, since they have a guanidine chelating ligand. Both entropy and enthalpy thermodynamic properties are favored with Nα-long chain alkanoyl di basic amino acid alkyl ester salts due to their potential formation of 5 and 6 membered rings with heavy metal ions. Furthermore, Nα-long chain alkanoyl di basic amino acid alkyl ester salts readily react with anionic species e.g., carboxylates, acidic amino acids, proteins having a residual negative charge, phosphato groups on nucleotides of DNA, anionic phospholipids, hydroxycarboxylates, phenolates, phosphonates, and phosphinates to give salts of low water solubility.
The second component of the synergistic system of this invention is a glyceryl monoalkanoate ester (acyl monoglyceride) having from 6 to 14 carbon atoms. Glyceryl monoalkanoates have a long history of safety and a low toxicity profile.
The literature is replete with numerous references concerning glycerol monofatty acid esters having antiviral and antibacterial activity. The most active monoglycerides consist of those esters formed from saturated fatty acids having from 6 to 14 carbon atoms. U.S. Pat. No. 4,997,851 teaches the use of saturated fatty acids and glycerol monofatty acid esters as effective antiviral agents against the HIV and HSV-1 viruses. They were also active against a variety of gram positive and gram-negative bacteria. U.S. Pat. No. 5,434,182 discloses the spermicidal, antimicrobial and cytocidal activity of glycerol monofatty acid esters.
It discloses the combination of fatty acyl glycerides, a chelating acid, and a surfactant which confer excellent antimicrobial activity for preserving processed meats and for disinfecting poultry carcasses. When only one of these three agents was used, the anti-microbial performance was considerably reduced. U.S. Pat. No. 6,414,023 B1 discloses the use of fatty acid monoglycerides in conjunction with 2,4-dichlorobenzyl alcohol.
John J. Kabara in U.S. Pat. No. 6,638,978 B1 lists a preservative formulation for food and cosmetics consisting of monolaurin (ML), caprylic and capric acid mixture, and propylene glycol in an aqueous base. U.S. 2005/0084471 A1 teaches the preparation of a preservative for meat, fruits, and vegetables and for the disinfection of inanimate surfaces. The actives include a propylene glycol C7-C14 fatty acid ester as the major component, a surfactant, and an enhancer. Enhancers include phenolic antioxidants and/or a paraben ester. Lastly, U.S. Patent 2006/0030512 A1 describes a long lasting anti-microbial film comprising a glycerol monoester, an amphoteric surfactant, a chelating agent and a solvent like propyl alcohol plus other incipients. All of the above references are incorporated into the body of our present invention.